Bob Lambert cradles his son in the maternity ward. The child’s mother said he was initially doting but later vanished from her life. Photograph: Guardian

A woman who had a child with an undercover police officer who was spying on her says she feels she was "raped by the state" and has been deeply traumatised after discovering his real identity.

She met the undercover officer – Bob Lambert – in 1984. At the time, Lambert was posing as "Bob Robinson", an animal rights activist, on behalf of the then secret police unit known as the Special Demonstration Squad (SDS).

The woman, whose first name is Jacqui, said Lambert was supportive when she became pregnant with their son in 1985, and wanted to have the child. But he later vanished from her life, claiming to be on the run. She only discovered his true identity last year – after spotting his photograph in a newspaper.

"I feel like I've got no foundations in my life," she said. "It was all built on sand – your first serious relationship, your first child, the first time you give birth – they're all significant, but for me they're gone, ruined, spoiled ...

"I was not consenting to sleeping with Bob Lambert, I didn't know who Bob Lambert was. I had a spy living with me, sleeping with me, making a family with me, and I didn't do anything to deserve that."

Jacqui gave the Guardian and Channel 4 an exclusive interview, parts of which were broadcast in a Dispatches documentary on Monday.

Her story is also recounted in the book at the centre of the latest revelations, Undercover: The Truth About Britain's Secret Police.

"I was 22 when I first met Bob Robinson. He was quite a bit older than me," she said. "He was very charming and charismatic and after only a couple of meetings I was smitten.

"Bob could be whatever you wanted him to be – and I wanted a man to love me. That's what Bob gave me. I always thought that he was besotted with me ... Most of the time we went to animal rights meetings in east London because that's who he wanted to be introduced to."

Lambert was spending several days a week with Jacqui while occasionally returning to his real wife and two children. Jacqui believes she was deliberately targeted because of her connections in the animal rights movement. "I think I was trusted and liked so no one ever questioned him because he was with me."

As the couple grew closer, Jacqui said she told him she wanted to have a child. "Since all this has come out I've been asked, didn't Bob try to get you to terminate the pregnancy? I have to make them understand that it was a planned pregnancy so why would he try to persuade me not to have the baby?"

A photograph of Lambert in the maternity ward shows him holding his son. "I now know that the Sunday I went into labour, he was spending that weekend with his wife and two young children. And all the time he knew that he was going to watch his girlfriend give birth to their child."

When their son was born, Jacqui said Lambert was initially a doting father. However, she believes she ceased to be useful to Lambert, who started to drift away. "Once I became a mum I cut back on doing all the animal stuff and I was no longer any use to him," she said.

During his five-year deployment, Lambert also infiltrated the environmental campaign group London Greenpeace. On Friday the Guardian revealed how he co-wrote the "McLibel leaflet", which defamed McDonald's and became the subject of the longest libel trial in English legal history.

After his deployment ended in 1988, Lambert went on to become a detective inspector in the SDS, where he supervised other undercover police spies. Former SDS officer and whistleblower Peter Francis said that Lambert advised him to wear a condom when sleeping with activists.

Lambert, who now works as a university academic, declined to comment on specific testimony from Jacqui or Francis. However in a general statement, he said allegations against him were a "combination of truth, distortions, exaggerations and outright lies".

He added: "The work of an undercover officer is complex, dangerous and sensitive and it would take some considerable time, and the co-operation of my former police employers, to provide the full background, context and detail necessary to address the matters which have been raised."

Jacqui tracked down Lambert and spoke with him last summer, after discovering – after 24 years – that the father of her son was a police infiltrator. All the time Lambert was actually working a few miles away from her, at Scotland Yard. "When I spoke to him I was saying, 'Why me?'" she said. "I gave out a few leaflets, went on a few demos, but I wasn't a bad person."

The former officer is since understood to have developed a relationship with his son, who has declined to be interviewed and asked for journalists to respect his privacy.

Jacqui is one of about a dozen women bringing a legal action against the Met for the trauma caused by long-term relationships with undercover police. She said: "We [the women bringing cases] are psychologically damaged; it is like being raped by the state. We feel that we were sexually abused because none of us gave consent."

She added: "I've had apologies from Bob himself but I want an apology from the organisation that paid him and gave him the orders."